The present invention relates to a warp-knitted fabric used in an inflatable belt cover for covering an envelope-like belt of an inflatable belt device. The envelope-like belt is a part of a seat belt and is inflatable with gas from a gas generator for protecting an occupant of a vehicle in a vehicle collision.
In Japanese Patent Application No. H09-23903, hereinafter referred to as the xe2x80x9c""903 applicationxe2x80x9d, the applicant of this invention has previously proposed an inflatable belt device which comprises an inflatable belt and a gas generator which supplies gas into the inflatable belt to inflate the inflatable belt. The inflatable belt comprises an envelope-like belt folded in a band-like configuration and a cover surrounding the envelope-like belt. The cover is hard to stretch in the longitudinal direction, but is stretchable in the inflating direction of the inflatable belt. This stretch of the inflatable belt in the inflating direction shortens the length of the inflatable belt in the longitudinal direction.
This inflatable belt device of the ""903 application will now be described with reference to the attached drawings. FIG. 1(a) is a perspective view illustrating a vehicle cabin equipped with an inflatable belt device of the ""903 application. FIG. 1(b) is a perspective view showing the inflatable belt device. FIG. 2(a) is a plan view showing a portion of the inflatable belt device at the connection between an inflatable belt and a webbing. FIG. 2(b) is a plan view showing an envelope-like belt. FIGS. 2(c), 2(d), 2(e) are sectional views taken along lines Cxe2x80x94C, Dxe2x80x94D, and Exe2x80x94E of FIG. 2(a), respectively. FIG. 3(a) is a plan view showing a shoulder belt in a state where the inflatable belt is inflated. FIG. 3(b) is a plan view showing the envelope-like belt in the inflated state. FIGS. 3(c) and 3(d) are sectional views taken along lines Cxe2x80x94C and Dxe2x80x94D of FIG. 3(a), respectively. FIGS. 4(a) and 4(b) are views for explaining a way of knitting a cover for the inflatable belt.
As shown in FIG. 1, this inflatable belt system 1 comprises a shoulder belt 2 extending diagonally from the right side to the left side of an occupant, a lap belt 3 extending from the right side to the left side of the occupant, a buckle unit 4 fixed to a vehicle floor or the like, a tongue 5 to be inserted into and engaged with the buckle unit 4 when the belt is about to be worn, and an intermediate guide 6 for guiding the shoulder belt 2.
The shoulder belt 2 comprises a webbing 2A which is the same as in a typical conventional seat belt, i.e. a normal belt, and an inflatable belt 2B connected to an end of the webbing 2A. The webbing 2A is slidably hung on the intermediate guide 6. The other end of the webbing 2A is connected to a seat belt retractor 7 with an emergency locking mechanism (ELR), which is fixed to the vehicle body. The webbing 2A is arranged in such a manner as to be wound into the seat belt retractor 7.
The inflatable belt 2B is positioned to be in contact with the occupant, and is connected to the tongue 5 at an end opposite to the end connected to the webbing 2A.
The lap belt 3 comprises a normal belt which is the same as in a typical conventional seat belt, of which one end is connected to the tongue 5 and the other end is connected to the seat belt retractor (ELR) 8, which is fixed to the vehicle body. Further, connected to the buckle unit 4 is a gas generator 9 which acts in the case of an emergency such as a vehicle collision and generates high pressure gas.
The tongue 5 and the buckle unit 4 are provided with passages for introducing gas from the gas generator 9 into the inflatable belt 2B.
As shown in FIGS. 2(a) through 3(d), the inflatable belt 2B comprises an envelope-like belt 10 and a cylindrical knit cover 12 surrounding the envelope-like belt 10. The envelope-like belt 10 has a wide portion corresponding to the chest and waist of the occupant sitting on the vehicle seat. The envelope-like belt 10 is folded into a shape of a band by folding the wide portion as shown in FIG. 2(b). The envelope-like belt 10 is stitched together with stitches 11.
The knit cover 12 is supplely stretchable in the lateral (course) direction, but is hard to stretch in the longitudinal (course) direction. FIGS. 4(a) and 4(b) illustrate ways of knitting this knit cover, respectively.
FIG. 4(a) illustrates a general way of warp-knitting of yarns 20 wherein a plurality of yarns 20 (20A-20D) form loops R. Each yarn 20 extends upwardly to make loops R on the left side and the right side alternately. Each yarn 20 extends in such a manner that the upper end of each loop R (for example, the upper end of a loop RB2) is twined around the root of one of the adjacent loops (for example, the root loop RA1) and the root of each loop R (for example, the root of the loop RB2) is twined by the upper end of one of the adjacent loops (for example, the upper end of a loop RA3). Therefore, the loops R are arranged to be continued in the vertical direction in the drawing and loops of a left-side yarn and loops of a right-side yarn are alternated in the vertical direction. That is, the loop RA1, the loop RB2, and the loop RA3 are arranged downwardly in this order.
FIG. 4(b) shows a way of warp-knitting wherein insert yarns 30 are knitted in addition to the yarns 20 to increase the strength of an obtained fabric and to reduce the thickness of the obtained fabric. Each insert yarn 30 is knitted in such a manner as to extend along a vertical array of loops and pass through intersections of loops on the front and the back alternately. As shown in FIG. 4(b), each insert yarn 30 is twined about one vertical array of loops.
The inflatable belt 2B and the lap belt 3 are connected to the tongue. The knit cover 12 is attached to both the webbing 2A and the tongue 5 so that the knit cover 12 is subjected to tension load applied to the inflatable belt.
As the gas generator 9 is actuated when the tongue 5 is latched to the buckle unit 4, the inflatable belt 2B is inflated. During the inflation, the knit cover 12 is shortened in the longitudinal direction of the inflatable belt 2B so that the inflatable belt 2B is tightened against the occupant, thereby securely protecting the occupant.
FIG. 5(a) shows the normal state where the knit cover. FIG. 5(b) shows a state where the knit cover 12 made of the warp-knitted fabric using the insert yarns 30 shown in FIG. 4(b) is shortened in the longitudinal (course) direction and lengthened in the lateral (wales) direction when the inflatable belt 2B (the envelope-like belt 10) is inflated. As mentioned above, the knit cover 12 has been processed by a heat-stretching process whereby the knit cover 12 is hard to stretch in the longitudinal direction. Therefore, when the envelope-like belt 10 is inflated, the knitted loops of the knit cover 12 are elongated in the lateral direction with the result that the length of the knit cover 12 is shortened in the longitudinal direction, shortening the length of the inflatable belt 2B.
In the inflatable belt device, when the inflatable belt is inflated as the gas generator is actuated, the cover is also inflated. Since the cover is hard to stretch in the longitudinal direction of the inflatable belt, the length of the cover is shortened during the inflation of the inflatable belt. The length of the inflatable belt is also shortened according to the shortening of the cover. As a result of this shortening, the inflatable belt is strongly fitted to the occupant, thereby securely protecting the occupant.
FIGS. 7(a)-7(c) are schematic views illustrating states in which xe2x80x9crunxe2x80x9d is caused in a comparative example without insert yarns. As a yarn is cut in the state shown in FIG. 7(a) and one twin of the loop is cancelled, loops are successively disengaged and the torn portion thus extends as shown in FIGS. 7(b), 7(c). By adding insert yarns into such a fabric, such extension of a torn portion can be prevented.
It is therefore an object of the present invention to improve the resistance to run (laddering) of a warp-knitted fabric for an inflatable belt cover with insert yarns.
The present invention is a warp-knitted fabric for an inflatable belt cover for covering an envelope-like belt which composes an inflatable belt that is folded into the shape of a band. The warp-knitted fabric comprises knitting yarns and insert yarns inserted among the knitting yarns. Each insert yarn is twined to pass through three or more vertical arrays of loops. At least two continuous loops are formed by chain-stitching a knitting yarn to compose a base knit structure.
In the warp-knitted fabric for an inflatable belt cover of the present invention, each insert yarn is twined to pass through three or more vertical arrays of loops and at least two continuous loops are formed by chain-stitching a knitting yarn to compose a base knit structure, thereby obtaining significantly improved resistance to xe2x80x9crunxe2x80x9d of fabric.